"They're popular with families who celebrate Valentine's Day together," she said.

The traditional deep-dish pizzas at Lou Malnati's, a family-run pizzeria chain in Chicago, already sell well on any given day.

But weeks before Valentine's Day, their heart-shaped pizza becomes the favorite with Chicagoans and consumers nationwide.

"Valentine's Day is now our second-busiest event behind the holiday season," said Meggie Eck, marketing manager for the 41-year-old family-owned Lou Malnati's.

She credits Rick Malnati, the founder's son, with coming up with the idea 22 years ago.

Rick, a basketball coach at Loyola University, thought it would be clever to create a heart-shaped pizza and initially tried to make it with a cookie cutter, said Eck. Eventually, he found a heart-shaped pan, and those pans are still used today.